---
title: Change comment
description: A change comment operation changes the comment on a column.
---

## Structure

<YamlJsonTabs>
```yaml
alter_column:
  table: table name
  column: column name
  comment: new comment for column | null
  up: SQL expression
  down: SQL expression
```
```json
{
  "alter_column": {
    "table": "table name",
    "column": "column name",
    "comment": "new comment for column" | null,
    "up": "SQL expression",
    "down": "SQL expression"
  }
}
```
</YamlJsonTabs>

The comment is added directly to the column on migration start.

## Examples

### Alter many column properties

An alter column migration performs many operations, including setting a comment:

<ExampleSnippet example="35_alter_column_multiple.yaml" languange="yaml" />

### Remove a comment

To remove a comment from a column set `comment` to `NULL`:

<ExampleSnippet example="36_set_comment_to_null.yaml" languange="yaml" />
